physics & astronomy

The role of binary star evolution and stochastic fluctuations in modeling stellar populations

I will discuss state of the art population synthesis models that improve on the following aspects with respect to most available models. (a) Treatment of the UV spectral range, including new evolutionary tracks and updated treatment of the ionizing radiation emitted by the stellar population. (b) Improved treatment of TP-AGB stars that dominate the NIR spectral range.  (c) Definition of new diagnostics to characterize the combined stellar and nebular emission and the cold ISM in galaxies. (d) The role of interacting binary stars on the integrated spectra of stellar populations will be discussed and compared with the effects produced by stochastic fluctuations in low mass populations. Single star models are available in a wide range of metallicity, from Z = 0 to Z = 0.06, and are ready to use to interpret the spectra of galaxies of any age at low and high redshift. Applications will be discussed.
Date: 
Thursday, March 5, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

Hui Li

Date: 
Thursday, March 26, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

David Stark

Date: 
Thursday, May 7, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
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Dark Energy Survey Data at the Low Surface Brightness Regime: Diffuse Light in Galaxies and Galaxy Clusters

The enormous amount of data collected by the Dark Energy Survey (DES) provide a great opportunity to explore low surface brightness science topics, such as faint diffuse light in galaxies and galaxy clusters. In this talk, I will describe how we study diffuse intra-cluster light through stacking the images of hundreds of galaxy clusters from DES, reaching a surface brightness limit of 30 mag/arcsec^2, out to a radial distance of 1 Mpc from the cluster center. Despite their low surface brightness, our studies show that intra-cluster light is a significant component of the galaxy cluster stellar content. The stacking method has also been applied to characterizing the light profiles of luminous red galaxies, as well as studying the aureole component of the DES point spread function. Weak lensing and precision photometry calibration  methods may wish to consider these effects in the future.
Date: 
Thursday, February 27, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

Jeong-Gyu Kim

Date: 
Thursday, April 30, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
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Long-term Monitoring of Active Galactic Nuclei with the NASA Swift mission.

I will report on long-term monitoring campaign with the NASA Swift mission.
Besides the the NASA Flagship missions Chandra and HST, Swift is NASA's Number 1 mission.
While Swift was launched more than 15 years ago as a Gamma Ray Burst observatory
over the last decade it has morphed into the major tool for time-domain Astrophysics
including studies of Active Galactic Nuclei (AGN). These super-massive accreting black holes
in the center of galaxies are the most luminous persistent object in Universe. However, many
of these AGN display dramatic flux variations on the UV and X-rays which can be explain for
example by absorption and dramatic changes in the accretion rate.
In my talk I will first introduce the NASA Swift observatory and its achivement for Astrophysics
before I will discuss the results of AGN studies with Swift.
Date: 
Thursday, January 30, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
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The Milky Way in its Extragalactic Context

In recent work, we have obtained improved measurements of the properties of the Milky Way and used the results to select a sample of Milky Way analog (MWA) galaxies from the Sloan Digital Sky Survey (SDSS) whose distributions of stellar mass and star formation rate match our Galaxy’s, incorporating all uncertainties. Relying on the Copernican assumption that the Milky Way should not be extraordinary, the colors and luminosities of the MWAs constrain the possible properties of our own Galaxy. This has enabled us to explore how our Galaxy fits in with the broader population; for instance, we can determine whether its properties are consistent with the power-law scaling relations exhibited by other spiral galaxies. The results have significant implications for the development of computational models of galaxy evolution in a cosmological context.  I will also describe follow-up work exploring the population of satellite galaxies in Milky Way-like dark matter halos.  It has been a long-standing puzzle why the Milky Way has considerably fewer satellite galaxies discovered to date than the typical number of satellite dark matter halos that would be found in a dark matter halo as massive as that which contains our Galaxy.  I will show that almost half of this ‘missing satellites’ problem can be explained by well-established ways in which our Galaxy’s dark matter halo is atypical.  Finally, if time allows I will also describe new work on the density profile of dark matter halos when mass within subhalos, which can often host individual galaxies, is not counted as part of the parent halo.  Widely-used profiles (such as Navarro Frenk and White) perform poorly at representing the smooth centrally-concentrated component of the halo, but there are simple functional forms which do better.
Date: 
Thursday, April 23, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
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A New Mask for An Old Suspect -- Testing the Sensitivity of the Galactic Center Excess to the Point Source Mask

The Galactic center excess has lingered as a possible, but ambiguous, signal of new physics for several years. It has previously been argued that certain details of the excess emission imply that it likely originates from a population of point sources, but this remains a topic of vigorous debate. In this talk, I will report on my recent work, relying on a new point source catalog (obtained by the Fermi-LAT collaboration), that sheds light on this controversial topic. After giving some background on the excess, I will discuss various metrics that have been used to try to understand its true nature. I will show that the large majority of bright sources that were previously suggested to be members of the excess are indeed contained in the new Fermi-LAT point source catalog -- and yet, despite masking out these sources (so that they cannot contribute to the excess), the excess remains just as bright in our new fit to the data. I will go on to discuss the implications of our findings for the two most popular interpretations of the excess.

Date: 
Thursday, December 19, 2019 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

Confronting Anomalies at Reactor Antineutrino Experiments

Date: 
Thursday, September 12, 2019 - 2:00pm to 3:00pm
Location: 
CP 179
Type of Event (for grouping events):

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